diff --git a/synapse/api/auth_blocking.py b/synapse/api/auth_blocking.py
new file mode 100644
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+++ b/synapse/api/auth_blocking.py
@@ -0,0 +1,104 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+from twisted.internet import defer
+
+from synapse.api.constants import LimitBlockingTypes, UserTypes
+from synapse.api.errors import Codes, ResourceLimitError
+from synapse.config.server import is_threepid_reserved
+
+logger = logging.getLogger(__name__)
+
+
+class AuthBlocking(object):
+ def __init__(self, hs):
+ self.store = hs.get_datastore()
+
+ self._server_notices_mxid = hs.config.server_notices_mxid
+ self._hs_disabled = hs.config.hs_disabled
+ self._hs_disabled_message = hs.config.hs_disabled_message
+ self._admin_contact = hs.config.admin_contact
+ self._max_mau_value = hs.config.max_mau_value
+ self._limit_usage_by_mau = hs.config.limit_usage_by_mau
+ self._mau_limits_reserved_threepids = hs.config.mau_limits_reserved_threepids
+
+ @defer.inlineCallbacks
+ def check_auth_blocking(self, user_id=None, threepid=None, user_type=None):
+ """Checks if the user should be rejected for some external reason,
+ such as monthly active user limiting or global disable flag
+
+ Args:
+ user_id(str|None): If present, checks for presence against existing
+ MAU cohort
+
+ threepid(dict|None): If present, checks for presence against configured
+ reserved threepid. Used in cases where the user is trying register
+ with a MAU blocked server, normally they would be rejected but their
+ threepid is on the reserved list. user_id and
+ threepid should never be set at the same time.
+
+ user_type(str|None): If present, is used to decide whether to check against
+ certain blocking reasons like MAU.
+ """
+
+ # Never fail an auth check for the server notices users or support user
+ # This can be a problem where event creation is prohibited due to blocking
+ if user_id is not None:
+ if user_id == self._server_notices_mxid:
+ return
+ if (yield self.store.is_support_user(user_id)):
+ return
+
+ if self._hs_disabled:
+ raise ResourceLimitError(
+ 403,
+ self._hs_disabled_message,
+ errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+ admin_contact=self._admin_contact,
+ limit_type=LimitBlockingTypes.HS_DISABLED,
+ )
+ if self._limit_usage_by_mau is True:
+ assert not (user_id and threepid)
+
+ # If the user is already part of the MAU cohort or a trial user
+ if user_id:
+ timestamp = yield self.store.user_last_seen_monthly_active(user_id)
+ if timestamp:
+ return
+
+ is_trial = yield self.store.is_trial_user(user_id)
+ if is_trial:
+ return
+ elif threepid:
+ # If the user does not exist yet, but is signing up with a
+ # reserved threepid then pass auth check
+ if is_threepid_reserved(self._mau_limits_reserved_threepids, threepid):
+ return
+ elif user_type == UserTypes.SUPPORT:
+ # If the user does not exist yet and is of type "support",
+ # allow registration. Support users are excluded from MAU checks.
+ return
+ # Else if there is no room in the MAU bucket, bail
+ current_mau = yield self.store.get_monthly_active_count()
+ if current_mau >= self._max_mau_value:
+ raise ResourceLimitError(
+ 403,
+ "Monthly Active User Limit Exceeded",
+ admin_contact=self._admin_contact,
+ errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+ limit_type=LimitBlockingTypes.MONTHLY_ACTIVE_USER,
+ )
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